Reduced Heat Capacity Research Articles

Copper/carbon core shell nanoparticles as additive for natural fiber/wood plastic blends

Copper/carbon core/shell nanoparticles (CCCSNs) recently have been introduced as an industrial material. In this paper, composites based on high density polyethylene (HDPE), bamboo fiber, CCCSNs, and coupling agent (MAPE) were prepared by melt compounding. The influence of CCCSN content on the resulting composites’ mechanical, biological resistance, and thermal properties was investigated. It was found that CCCSNs within the carbon black matrix were processed well with bamboo fiber-plastic blends through mixing and injection molding. The materials enhanced composite strength and modulus-related properties. Composites with CCCSNs and natural fibers reduced heat capacity and thermal diffusivity. Composites with CCCSN materials also enhanced termite and mold performance. Thus, the material can be used as additive for plastics and other polymers to modify strength properties, biological resistance (e.g., mold and stain), and thermal conductivity properties.

Determination of the magnetic contribution to the heat capacity of cobalt oxidenanoparticles and the thermodynamic properties of the hydration layers

We present low temperature (11 K) inelastic neutron scattering(INS) data on four hydrated nanoparticle systems: 10 nmCoO·0.10H2O (1), 16 nmCo3O4·0.40H2O (2), 25 nmCo3O4·0.30H2O (3) and40 nm Co3O4·0.026H2O (4). The vibrational densities of states were obtained for all samples and from these theisochoric heat capacity and vibrational energy for the hydration layers confined to the surfacesof these nanoparticle systems have been elucidated. The results show that water on thesurface of CoO nanoparticles is more tightly bound than water confined to the surface ofCo3O4, andthis is reflected in the reduced heat capacity and vibrational entropy for water on CoO relative to wateron Co3O4 nanoparticles. This supports the trend, seen previously, for water to be more tightly boundin materials with higher surface energies. The INS spectra for the antiferromagneticCo3O4 particles (2–4) also show sharp and intense magnetic excitation peaks at5 meV, and from this the magnetic contribution to the heat capacity ofCo3O4 nanoparticles has been calculated; this represents the first example of use of INS data fordetermining the magnetic contribution to the heat capacity of any magnetic nanoparticlesystem.

Dynamics near the filler surface in natural rubber-silica nanocomposites

We study the effect of in situ synthesized 10 nm silica nanoparticles on the glass transition and dynamics of natural rubber networks using differential scanning calorimetry, broadband dielectric relaxation spectroscopy and thermally stimulated depolarization currents. Even in the absence of specific polymer-filler interactions, polymer segments within a few nanometers of the filler particles exhibit relaxation times up to 2–3 orders of magnitude slower and reduced heat capacity increment at the glass transition compared to bulk natural rubber. These effects are only observed when the nanoparticles are uniformly distributed in the polymer matrix.

Influence of Crystal Polymorphism on the Three-Phase Structure and on the Thermal Properties of Isotactic Poly(1-butene)

The influence of crystal polymorphism on the three-phase structure of isotactic poly(1-butene) (PB-1) is discussed. Crystallization of PB-1 from the melt yields the tetragonal phase, known as form II. Upon storage, it spontaneously transforms to the trigonal form I. The chain motion within the crystalline parts varies strongly with the crystal structure and affects the coupled amorphous parts. The form II−form I solid−solid transformation is accompanied by a change in the thermal properties that involves all parts of the three-phase structure. The increased density and thermal stability of the crystals cause a higher rigidity of the coupled amorphous phases. In form I PB-1, the mobile amorphous phase (MAF) has a reduced heat capacity step at the glass-transition temperature that occurs at a slightly broadened temperature. The RAF is coupled more strongly to the rigid form I crystals and relaxes at higher temperatures compared with the polymer containing modification II crystals, which are conformationally disordered. Both polymorphs display only little reversibility of the melting process. It is almost negligible in form I PB-1 and more conspicuous in the form II crystals. The different behavior arises from the varied recrystallization kinetics, which is limited in extent for the trigonal polymorph.

Collapse-driven self-assembly of multiblock chains: A Monte Carlooff-lattice study

Abstract We perform off-lattice Monte Carlo simulations for multiblock chains, ( 5 A - 5 B ) n , with n = 10 , 20 , 30 , 40 , 50 , and 60 , in an implicit selective solvent, using a discontinuous square-well potential. We present selected thermodynamic and structural properties as a function of the reduced temperature, such as the reduced energy per segment, the reduced heat capacity, and the mean-squared radius of gyration. We observe that the collapse-driven self-assembled structure is not spherical above certain value of chain length, N, and develops a non-spherical globular structure with multiple cores.

Thermostable variants of the recombinant xylanase a from Bacillus subtilis produced by directed evolution show reduced heat capacity changes

Directed evolution techniques have been used to improve the thermal stability of the xylanase A from Bacillus subtilis (XylA). Two generations of random mutant libraries generated by error prone PCR coupled with a single generation of DNA shuffling produced a series of mutant proteins with increasing thermostability. The most Thermostable XylA variant from the third generation contained four mutations Q7H, G13R, S22P, and S179C that showed an increase in melting temperature of 20 degrees C. The thermodynamic properties of a representative subset of nine XylA variants showing a range of thermostabilities were measured by thermal denaturation as monitored by the change in the far ultraviolet circular dichroism signal. Analysis of the data from these thermostable variants demonstrated a correlation between the decrease in the heat capacity change (deltaC(p)) with an increase in the midpoint of the transition temperature (T(m)) on transition from the native to the unfolded state. This result could not be interpreted within the context of the changes in accessible surface area of the protein on transition from the native to unfolded states. Since all the mutations are located at the surface of the protein, these results suggest that an explanation of the decrease in deltaC(p) should include effects arising from the protein/solvent interface.

Formula omitted]: Enhanced low-energy excitations of electrons on a 2d triangular lattice

To elucidate the low-energy excitation spectrum of correlated electrons on a 2D triangular lattice, we have studied the electrical resistance and specific heat down to 0.5 K and in magnetic fields up to 14 T , in Na x CoO 2 samples with a Na content ranging from x ≈ 0.5 to 0.82 . Two distinct regimes are observed: for x from about 0.64 to x ≈ 0.75 the specific heat is strongly enhanced, with a pronounced upturn of C p / T below about 10 K , reaching 47 mJ / ( mol K 2 ) . This enhancement is suppressed in a magnetic field indicative of strong low-energy spin fluctuations. At higher Na content, the fluctuations are reduced and μ SR data confirm the SDW ground state below 22 K and the much reduced heat capacity is field independent.

Electrostatic Interactions Contribute to Reduced Heat Capacity Change of Unfolding in a Thermophilic Ribosomal Protein L30e

The origin of reduced heat capacity change of unfolding (DeltaC(p)) commonly observed in thermophilic proteins is controversial. The established theory that DeltaC(p) is correlated with change of solvent-accessible surface area cannot account for the large differences in DeltaC(p) observed for thermophilic and mesophilic homologous proteins, which are very similar in structures. We have determined the protein stability curves, which describe the temperature dependency of the free energy change of unfolding, for a thermophilic ribosomal protein L30e from Thermococcus celer, and its mesophilic homologue from yeast. Values of DeltaC(p), obtained by fitting the free energy change of unfolding to the Gibbs-Helmholtz equation, were 5.3 kJ mol(-1) K(-1) and 10.5 kJ mol(-1) K(-1) for T.celer and yeast L30e, respectively. We have created six charge-to-neutral mutants of T.celer L30e. Removal of charges at Glu6, Lys9, and Arg92 decreased the melting temperatures of T.celer L30e by approximately 3-9 degrees C, and the differences in melting temperatures were smaller with increasing concentration of salt. These results suggest that these mutations destabilize T.celer L30e by disrupting favorable electrostatic interactions. To determine whether electrostatic interactions contribute to the reduced DeltaC(p) of the thermophilic protein, we have determined DeltaC(p) for wild-type and mutant T.celer L30e by Gibbs-Helmholtz and by van't Hoff analyses. A concomitant increase in DeltaC(p) was observed for those charge-to-neutral mutants that destabilize T.celer L30e by removing favorable electrostatic interactions. The crystal structures of K9A, E90A, and R92A, were determined, and no structural change was observed. Taken together, our results support the conclusion that electrostatic interactions contribute to the reduced DeltaC(p) of T.celer L30e.

Toward the Physical Basis of Thermophilic Proteins: Linking of Enriched Polar Interactions and Reduced Heat Capacity of Unfolding

The enrichment of salt bridges and hydrogen bonding in thermophilic proteins has long been recognized. Another tendency, featuring lower heat capacity of unfolding (Δ C p) than found in mesophilic proteins, is emerging from the recent literature. Here we present a simple electrostatic model to illustrate that formation of a salt-bridge or hydrogen-bonding network around an ionized group in the folded state leads to increased folding stability and decreased Δ C p. We thus suggest that the reduced Δ C p of thermophilic proteins could partly be attributed to enriched polar interactions. A reduced Δ C p might serve as an indicator for the contribution of polar interactions to folding stability.

Conformational stability of adrenodoxin mutant proteins.

Adrenodoxin and the mutants at the positions T54, H56, D76, Y82, and C95, as well as the deletion mutants 4-114 and 4-108, were studied by high-sensitivity scanning microcalorimetry, limited proteolysis, and absorption spectroscopy. The mutants show thermal transition temperatures ranging from 46 to 56 degrees C, enthalpy changes from 250 to 370 kJ/mol, and heat capacity change delta Cp = 7.28 +/- 0.67 kJ/mol/K, except H56R. The amino acid replacement H56R produces substantial local changes in the region around positions 56 and Y82, as indicated by reduced heat capacity change (delta Cp = 4.29 +/- 0.37 kJ/mol/K) and enhanced fluorescence. Deletion mutant 4-108 is apparently more stable than the wild type, as judged by higher specific denaturation enthalpy and resistance toward proteolytic degradation. No simple correlation between conformational stability and functional properties could be found.

The formation of electron-temperature hot spots in the main ionospheric trough by the internal processes

Abstract. A mathematical model of the convecting high-latitude ionosphere is described which produces three-dimensional distributions of electron density, positive-ion velocity and electron and ion temperatures at the F-layer altitudes. The results of simulation of the behaviour of the high-latitude ionosphere, in particular, the heat regime of the F-layer, are presented and analysed. From our study, it was found that electron-temperature hot spots in the main ionospheric trough can arise owing to internal ionospheric processes, and not due to effects of any external causes. Three conditions, to be satisfied simultaneously, are necessary for the formation of the considered electron-temperature hot spots: first, low values of electron density; second, solar illumination of the upper F region and darkness of the lower F region; third, low values of neutral-component densities. These conditions are valid in the main ionospheric trough near the terminator on the nightside when the density of the neutral atmosphere is not high. The physical processes which lead to the formation of the electron-temperature hot spots are the heat transfer from the upper into the lower F region, the reduced heat capacity of electron gas and the weakened cooling of electron gas due to inelastic collisions with neutral atoms and molecules. Also investigated is the influence of seasonal and solar-activity variations on the efficiency of the identified mechanism responsible for the formation of the electron temperature peaks in the main ionospheric trough by the internal processes.

Effect of Elevated Curing Temperature on the Chloride Permeability of High-Strength Lightweight Concrete

Abstract Due to high cement contents and reduced heat capacity, high-strength lightweight concrete is often exposed to elevated curing temperatures. In the production of lightweight concrete the aggregate is often wetted before use, but sometimes dry aggregate is also applied. In order to find out whether elevated curing temperatures in combination with varying moisture conditions of the aggregate would affect the concrete permeability, an experimental investigation was carried out. The results showed that maximum curing temperatures of up to 80°C did not adversely affect the compressive strength when dry aggregate was used, while a temperature above 50°C reduced the compressive strength when wet aggregate was employed. Temperatures above 65°C increased the permeability in both cases of aggregate moisture condition. At 20°C the compressive strength was higher for the wet aggregate concrete (103.8 MPa) compared to that of the dry aggregate concrete (95.3 MPa), but the permeability was also higher for the wet aggregate concrete (150%). When all the moisture was removed at 105°C, the wet aggregate concrete absorbed approximately 15% more water by capillary absorption than the dry aggregate concrete. Backscattered electron images showed a very dense transition zone between cement paste and aggregate both for the dry and the wet aggregate concrete.